This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Typically, the sorting of pieces of materials has involved determining a physical property or properties of each piece, and grouping together pieces sharing a common property or properties. Such properties may include color, hue, texture, weight, density, transmissivity to light, sound, or other signals, in reaction to stimuli such as various fields.
Scrap metals are often shredded, and thus require sorting to facilitate reuse of the metals. By sorting the scrap metals, metal is reused that may otherwise go to a landfill. Additionally, use of sorted scrap metal leads to reduced pollution and emissions in comparison to refining virgin feedstock from ore. Scrap metals may be used in place of virgin feedstock by manufacturers if the quality of the sorted metal meets certain standards. The scrap metals may include types of ferrous and nonferrous metals, heavy metals, high value metals such as nickel or titanium, cast or wrought metals, and other various alloys.
The recycling of nonferrous metals from shredded end-of-life equipment, such as cars or domestic appliances, is steadily increasing in importance, as many raw materials, such as copper or aluminum, can be recovered in this manner. However, for this to be possible, these fractions must be extracted to a high degree of purity. Therefore, an effective, efficient, and economical sorting process can add value because the market value of refined individual nonferrous fractions is significantly higher than that of unsorted ferrous mixtures.
The recycling of aluminum scrap is a very attractive proposition in that up to 95% of the energy costs can be saved when compared with the laborious extraction of the more costly primary aluminum. Primary aluminum is defined as aluminum originating from aluminum-enriched ore, such as bauxite. At the same time, the demand for aluminum is steadily increasing in markets, such as car manufacturing, because of its lightweight properties. Correspondingly, it is particularly desirable to efficiently separate aluminum scrap metals into alloy families, since mixed aluminum scrap of the same alloy family is worth much more than that of indiscriminately mixed alloys. For example, in the blending methods used to recycle aluminum, any quantity of scrap composed of similar, or the same, alloys and of consistent quality, has more value than scrap consisting of mixed aluminum alloys.
Wrought scrap contains a mixture of wrought alloys. The mixed wrought scrap has limited value because the mixture, due to its combined chemical composition, must be diluted if used to produce a new wrought alloy. The reason this is so is due to the more stringent compositional tolerances of wrought alloys, which are required to meet the performance requirements of wrought products. The high value scrap should have a high absorption back into the recycled product. High absorption means that a substantial portion of the final product is composed of scrap. To increase the value of the wrought scrap requires the separation of wrought product into alloy grades or similar constituted materials to maximize absorption. Mixed alloy scrap presents some difficult problems in separability due to its poor absorption into high quality wrought alloys. Mixed alloy scrap has poor absorption into high quality wrought alloys, and as a result, only limited amounts of mixed scrap can be used for recycling into wrought products. Absorption is defined as the percentage of an alloy or mixture that can be used to produce an ingot of another desired composition without exceeding the specified alloy composition limits. Within such aluminum alloys, aluminum will always be the bulk of the material. However, constituents such as copper, magnesium, silicon, iron, chromium, zinc, manganese, and other alloy elements provide a range of properties to alloyed aluminum and provide a means to distinguish one wrought alloy from the other.
The Aluminum Association is the authority which defines the allowable limits for aluminum alloy chemical composition. The data for the alloy chemical compositions is published by the Aluminum Association in “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys,” which was updated in January 2015, and which is incorporated by reference herein. The Aluminum Association also has a similar document for cast alloys. In general, according to the Aluminum Association, the 1000 series of aluminum alloys is composed essentially of pure aluminum with a minimum 99% aluminum content by weight; the 2000 series is aluminum principally alloyed with copper; the 3000 series is aluminum principally alloyed with manganese; the 4000 series is aluminum alloyed with silicon; the 5000 series is aluminum primarily alloyed with magnesium; the 6000 series is aluminum alloyed with magnesium and silicon; the 7000 series is aluminum primarily alloyed with zinc; and the 8000 series is a miscellaneous category.
While it would therefore be beneficial to be able to sort a mass or body of aluminum sheet scrap containing a heterogeneous mixture of pieces of different alloys, to separate the different alloy compositions or at least different alloy families before re-melting for recycling, scrap pieces of different aluminum alloy compositions are not ordinarily visually distinguishable from each other. Optically indistinguishable metals are difficult to sort and, therefore, might be lost. For example, it is not easy to manually separate and identify small pieces of cast from wrought aluminum or to spot zinc or steel attachments encapsulated in aluminum. There also is the problem that color sorting is nearly impossible for identically colored materials, such as the all-gray metals of aluminum alloys, zinc, and lead.
Furthermore, the presence of commingled pieces of different alloys in a body of scrap limits the ability of the scrap to be usefully recycled, unless the different alloys (or, at least, alloys belonging to different compositional families such as those designated by the Aluminum Association series 1000, 2000, 3000, etc.) can be separated prior to re-melting. This is because, when commingled scrap of plural different alloy compositions or composition families is re-melted, the resultant molten mixture contains proportions of the principle alloy and elements (or the different compositions) that are too high to satisfy the compositional limitations of any particular commercial alloy.
Moreover, as evidenced by the production and sale of the 2015 Ford F-150 pickup having a considerable increase in its body and frame parts consisting of aluminum instead of steel, it is additionally desirable to recycle sheet metal scrap, including that generated in the manufacture of automotive components from sheet aluminum. Recycling of the scrap involves re-melting the scrap to provide a body of molten metal that can be cast and/or rolled into useful aluminum parts for further production of such vehicles. However, automotive manufacturing scrap (and metal scrap from other sources such as airplanes and commercial and household appliances) often includes a mixture of scrap pieces of two or more aluminum alloys differing substantially from each other in composition. A specific example of mixed manufacturing scrap of aluminum sheet, generated in certain present-day automotive manufacturing operations, is a mixture of pieces of one or more alloys of the Aluminum Association 5000 series and pieces of one or more alloys of the Aluminum Association 6000 series. Thus, those skilled in the aluminum alloy art will appreciate the difficulties in this art of separating aluminum alloys, especially alloys that have been worked such as forged, extruded, rolled, and generally wrought alloys, into a reusable or recyclable worked product. These alloys for the most part are indistinguishable upon visual inspection or by other conventional scrap sorting techniques such as density and/or eddy-currents. Therefore, it is a difficult task to separate for example, 2000, 3000, 5000, 6000, and 7000 series alloys; moreover, the ability to sort between aluminum alloys within the same Aluminum Association series has not been accomplished in the prior art.
As a result, there are certain economies available to the aluminum industry by developing a well-planned yet simple recycling plan or system. The use of recycled material would be a less expensive metal resource than a primary source of aluminum. As the amount of aluminum sold to the automotive industry (and other industries) increases, it will become increasingly necessary to use recycled aluminum to supplement the availability of primary aluminum.